1. 26 Apr, 2022 2 commits
    • Madelyn Olson's avatar
      Set replicas to panic on disk errors, and optionally panic on replication errors (#10504) · 6fa8e4f7
      Madelyn Olson authored
      * Till now, replicas that were unable to persist, would still execute the commands
        they got from the master, now they'll panic by default, and we add a new
        `replica-ignore-disk-errors` config to change that.
      * Till now, when a command failed on a replica or AOF-loading, it only logged a
        warning and a stat, we add a new `propagation-error-behavior` config to allow
        panicking in that state (may become the default one day)
      
      Note that commands that fail on the replica can either indicate a bug that could
      cause data inconsistency between the replica and the master, or they could be
      in some cases (specifically in previous versions), a result of a command (e.g. EVAL)
      that failed on the master, but still had to be propagated to fail on the replica as well.
      6fa8e4f7
    • Madelyn Olson's avatar
      By default prevent cross slot operations in functions and scripts with # (#10615) · efcd1bf3
      Madelyn Olson authored
      Adds the `allow-cross-slot-keys` flag to Eval scripts and Functions to allow
      scripts to access keys from multiple slots.
      The default behavior is now that they are not allowed to do that (unlike before).
      This is a breaking change for 7.0 release candidates (to be part of 7.0.0), but
      not for previous redis releases since EVAL without shebang isn't doing this check.
      
      Note that the check is done on both the keys declared by the EVAL / FCALL command
      arguments, and also the ones used by the script when making a `redis.call`.
      
      A note about the implementation, there seems to have been some confusion
      about allowing access to non local keys. I thought I missed something in our
      wider conversation, but Redis scripts do block access to non-local keys.
      So the issue was just about cross slots being accessed.
      efcd1bf3
  2. 25 Apr, 2022 2 commits
  3. 11 Apr, 2022 1 commit
    • zhaozhao.zz's avatar
      Durability enhancement for appendfsync=always policy (#9678) · 1a7765cb
      zhaozhao.zz authored
      Durability of database is a big and old topic, in this regard Redis use AOF to
      support it, and `appendfsync=alwasys` policy is the most strict level, guarantee
      all data is both written and synced on disk before reply success to client.
      
      But there are some cases have been overlooked, and could lead to durability broken.
      
      1. The most clear one is about threaded-io mode
         we should also set client's write handler with `ae_barrier` in
         `handleClientsWithPendingWritesUsingThreads`, or the write handler would be
         called after read handler in the next event loop, it means the write command result
         could be replied to client before flush to AOF.
      2. About blocked client (mostly by module)
         in `beforeSleep()`, `handleClientsBlockedOnKeys()` should be called before
         `flushAppendOnlyFile()`, in case the unblocked clients modify data without persistence
         but send reply.
      3. When handling `ProcessingEventsWhileBlocked`
         normally it takes place when lua/function/module timeout, and we give a chance to users
         to kill the slow operation, but we should call `flushAppendOnlyFile()` before
         `handleClientsWithPendingWrites()`, in case the other clients in the last event loop get
         acknowledge before data persistence.
         for a instance:
         ```
         in the same event loop
         client A executes set foo bar
         client B executes eval "for var=1,10000000,1 do end" 0
         ```
         after the script timeout, client A will get `OK` but lose data after restart (kill redis when
         timeout) if we don't flush the write command to AOF.
      4. A more complex case about `ProcessingEventsWhileBlocked`
         it is lua timeout in transaction, for example
         `MULTI; set foo bar; eval "for var=1,10000000,1 do end" 0; EXEC`, then client will get set
         command's result before the whole transaction done, that breaks atomicity too.
         fortunately, it's already fixed by #5428 (although it's not the original purpose just a side
         effect : )), but module timeout should be fixed too.
      
      case 1, 2, 3 are fixed in this commit, the module issue in case 4 needs a followup PR.
      1a7765cb
  4. 10 Apr, 2022 1 commit
  5. 25 Mar, 2022 1 commit
    • zhaozhao.zz's avatar
      optimize(remove) usage of client's pending_querybuf (#10413) · 78bef6e1
      zhaozhao.zz authored
      To remove `pending_querybuf`, the key point is reusing `querybuf`, it means master client's `querybuf` is not only used to parse command, but also proxy to sub-replicas.
      
      1. add a new variable `repl_applied` for master client to record how many data applied (propagated via `replicationFeedStreamFromMasterStream()`) but not trimmed in `querybuf`.
      
      2. don't sdsrange `querybuf` in `commandProcessed()`, we trim it to `repl_applied` after the whole replication pipeline processed to avoid fragmented `sdsrange`. And here are some scenarios we cannot trim to `qb_pos`:
          * we don't receive complete command from master
          * master client blocked because of client pause
          * IO threads operate read, master client flagged with CLIENT_PENDING_COMMAND
      
          In these scenarios, `qb_pos` points to the part of the current command or the beginning of next command, and the current command is not applied yet, so the `repl_applied` is not equal to `qb_pos`.
      
      Some other notes:
      * Do not do big arg optimization on master client, since we can only sdsrange `querybuf` after data sent to replicas.
      * Set `qb_pos` and `repl_applied` to 0 when `freeClient` in `replicationCacheMaster`.
      * Rewrite `processPendingCommandsAndResetClient` to `processPendingCommandAndInputBuffer`, let `processInputBuffer` to be called successively after `processCommandAndResetClient`.
      78bef6e1
  6. 16 Mar, 2022 1 commit
  7. 15 Mar, 2022 1 commit
    • yoav-steinberg's avatar
      Optimization: remove `updateClientMemUsage` from i/o threads. (#10401) · cf6dcb7b
      yoav-steinberg authored
      In a benchmark we noticed we spend a relatively long time updating the client
      memory usage leading to performance degradation.
      Before #8687 this was performed in the client's cron and didn't affect performance.
      But since introducing client eviction we need to perform this after filling the input
      buffers and after processing commands. This also lead me to write this code to be
      thread safe and perform it in the i/o threads.
      
      It turns out that the main performance issue here is related to atomic operations
      being performed while updating the total clients memory usage stats used for client
      eviction (`server.stat_clients_type_memory[]`). This update needed to be atomic
      because `updateClientMemUsage()` was called from the IO threads.
      
      In this commit I make sure to call `updateClientMemUsage()` only from the main thread.
      In case of threaded IO I call it for each client during the "fan-in" phase of the read/write
      operation. This also means I could chuck the `updateClientMemUsageBucket()` function
      which was called during this phase and embed it into `updateClientMemUsage()`.
      
      Profiling shows this makes `updateClientMemUsage()` (on my x86_64 linux) roughly x4 faster.
      cf6dcb7b
  8. 13 Mar, 2022 1 commit
  9. 09 Mar, 2022 1 commit
  10. 08 Mar, 2022 1 commit
    • guybe7's avatar
      XREADGROUP: Unblock client if stream is deleted (#10306) · 2a295408
      guybe7 authored
      Deleting a stream while a client is blocked XREADGROUP should unblock the client.
      
      The idea is that if a client is blocked via XREADGROUP is different from
      any other blocking type in the sense that it depends on the existence of both
      the key and the group. Even if the key is deleted and then revived with XADD
      it won't help any clients blocked on XREADGROUP because the group no longer
      exist, so they would fail with -NOGROUP anyway.
      The conclusion is that it's better to unblock these clients (with error) upon
      the deletion of the key, rather than waiting for the first XADD. 
      
      Other changes:
      1. Slightly optimize all `serveClientsBlockedOn*` functions by checking `server.blocked_clients_by_type`
      2. All `serveClientsBlockedOn*` functions now use a list iterator rather than looking at `listFirst`, relying
        on `unblockClient` to delete the head of the list. Before this commit, only `serveClientsBlockedOnStreams`
        used to work like that.
      3. bugfix: CLIENT UNBLOCK ERROR should work even if the command doesn't have a timeout_callback
        (only relevant to module commands)
      2a295408
  11. 27 Feb, 2022 1 commit
    • Meir Shpilraien (Spielrein)'s avatar
      Sort out the mess around Lua error messages and error stats (#10329) · aa856b39
      Meir Shpilraien (Spielrein) authored
      
      
      This PR fix 2 issues on Lua scripting:
      * Server error reply statistics (some errors were counted twice).
      * Error code and error strings returning from scripts (error code was missing / misplaced).
      
      ## Statistics
      a Lua script user is considered part of the user application, a sophisticated transaction,
      so we want to count an error even if handled silently by the script, but when it is
      propagated outwards from the script we don't wanna count it twice. on the other hand,
      if the script decides to throw an error on its own (using `redis.error_reply`), we wanna
      count that too.
      Besides, we do count the `calls` in command statistics for the commands the script calls,
      we we should certainly also count `failed_calls`.
      So when a simple `eval "return redis.call('set','x','y')" 0` fails, it should count the failed call
      to both SET and EVAL, but the `errorstats` and `total_error_replies` should be counted only once.
      
      The PR changes the error object that is raised on errors. Instead of raising a simple Lua
      string, Redis will raise a Lua table in the following format:
      
      ```
      {
          err='<error message (including error code)>',
          source='<User source file name>',
          line='<line where the error happned>',
          ignore_error_stats_update=true/false,
      }
      ```
      
      The `luaPushError` function was modified to construct the new error table as describe above.
      The `luaRaiseError` was renamed to `luaError` and is now simply called `lua_error` to raise
      the table on the top of the Lua stack as the error object.
      The reason is that since its functionality is changed, in case some Redis branch / fork uses it,
      it's better to have a compilation error than a bug.
      
      The `source` and `line` fields are enriched by the error handler (if possible) and the
      `ignore_error_stats_update` is optional and if its not present then the default value is `false`.
      If `ignore_error_stats_update` is true, the error will not be counted on the error stats.
      
      When parsing Redis call reply, each error is translated to a Lua table on the format describe
      above and the `ignore_error_stats_update` field is set to `true` so we will not count errors
      twice (we counted this error when we invoke the command).
      
      The changes in this PR might have been considered as a breaking change for users that used
      Lua `pcall` function. Before, the error was a string and now its a table. To keep backward
      comparability the PR override the `pcall` implementation and extract the error message from
      the error table and return it.
      
      Example of the error stats update:
      
      ```
      127.0.0.1:6379> lpush l 1
      (integer) 2
      127.0.0.1:6379> eval "return redis.call('get', 'l')" 0
      (error) WRONGTYPE Operation against a key holding the wrong kind of value. script: e471b73f1ef44774987ab00bdf51f21fd9f7974a, on @user_script:1.
      
      127.0.0.1:6379> info Errorstats
      # Errorstats
      errorstat_WRONGTYPE:count=1
      
      127.0.0.1:6379> info commandstats
      # Commandstats
      cmdstat_eval:calls=1,usec=341,usec_per_call=341.00,rejected_calls=0,failed_calls=1
      cmdstat_info:calls=1,usec=35,usec_per_call=35.00,rejected_calls=0,failed_calls=0
      cmdstat_lpush:calls=1,usec=14,usec_per_call=14.00,rejected_calls=0,failed_calls=0
      cmdstat_get:calls=1,usec=10,usec_per_call=10.00,rejected_calls=0,failed_calls=1
      ```
      
      ## error message
      We can now construct the error message (sent as a reply to the user) from the error table,
      so this solves issues where the error message was malformed and the error code appeared
      in the middle of the error message:
      
      ```diff
      127.0.0.1:6379> eval "return redis.call('set','x','y')" 0
      -(error) ERR Error running script (call to 71e6319f97b0fe8bdfa1c5df3ce4489946dda479): @user_script:1: OOM command not allowed when used memory > 'maxmemory'.
      +(error) OOM command not allowed when used memory > 'maxmemory' @user_script:1. Error running script (call to 71e6319f97b0fe8bdfa1c5df3ce4489946dda479)
      ```
      
      ```diff
      127.0.0.1:6379> eval "redis.call('get', 'l')" 0
      -(error) ERR Error running script (call to f_8a705cfb9fb09515bfe57ca2bd84a5caee2cbbd1): @user_script:1: WRONGTYPE Operation against a key holding the wrong kind of value
      +(error) WRONGTYPE Operation against a key holding the wrong kind of value script: 8a705cfb9fb09515bfe57ca2bd84a5caee2cbbd1, on @user_script:1.
      ```
      
      Notica that `redis.pcall` was not change:
      ```
      127.0.0.1:6379> eval "return redis.pcall('get', 'l')" 0
      (error) WRONGTYPE Operation against a key holding the wrong kind of value
      ```
      
      
      ## other notes
      Notice that Some commands (like GEOADD) changes the cmd variable on the client stats so we
      can not count on it to update the command stats. In order to be able to update those stats correctly
      we needed to promote `realcmd` variable to be located on the client struct.
      
      Tests was added and modified to verify the changes.
      
      Related PR's: #10279, #10218, #10278, #10309
      Co-authored-by: default avatarOran Agra <oran@redislabs.com>
      aa856b39
  12. 24 Feb, 2022 1 commit
  13. 23 Feb, 2022 1 commit
  14. 22 Feb, 2022 2 commits
    • Andy Pan's avatar
      Reduce system calls of write for client->reply by introducing writev (#9934) · 496375fc
      Andy Pan authored
      There are scenarios where it results in many small objects in the reply list,
      such as commands heavily using deferred array replies (`addReplyDeferredLen`).
      E.g. what COMMAND command and CLUSTER SLOTS used to do (see #10056, #7123),
      but also in case of a transaction or a pipeline of commands that use just one differed array reply.
      
      We used to have to run multiple loops along with multiple calls to `write()` to send data back to
      peer based on the current code, but by means of `writev()`, we can gather those scattered
      objects in reply list and include the static reply buffer as well, then send it by one system call,
      that ought to achieve higher performance.
      
      In the case of TLS,  we simply check and concatenate buffers into one big buffer and send it
      away by one call to `connTLSWrite()`, if the amount of all buffers exceeds `NET_MAX_WRITES_PER_EVENT`,
      then invoke `connTLSWrite()` multiple times to avoid a huge massive of memory copies.
      
      Note that aside of reducing system calls, this change will also reduce the amount of
      small TCP packets sent.
      496375fc
    • ranshid's avatar
      introduce dynamic client reply buffer size - save memory on idle clients (#9822) · 47c51d0c
      ranshid authored
      
      
      Current implementation simple idle client which serves no traffic still
      use ~17Kb of memory. this is mainly due to a fixed size reply buffer
      currently set to 16kb.
      
      We have encountered some cases in which the server operates in a low memory environments.
      In such cases a user who wishes to create large connection pools to support potential burst period,
      will exhaust a large amount of memory  to maintain connected Idle clients.
      Some users may choose to "sacrifice" performance in order to save memory.
      
      This commit introduce a dynamic mechanism to shrink and expend the client reply buffer based on
      periodic observed peak.
      the algorithm works as follows:
      1. each time a client reply buffer has been fully written, the last recorded peak is updated: 
      new peak = MAX( last peak, current written size)
      2. during clients cron we check for each client if the last observed peak was:
           a. matching the current buffer size - in which case we expend (resize) the buffer size by 100%
           b. less than half the buffer size - in which case we shrink the buffer size by 50%
      3. In any case we will **not** resize the buffer in case:
          a. the current buffer peak is less then the current buffer usable size and higher than 1/2 the
            current buffer usable size
          b. the value of (current buffer usable size/2) is less than 1Kib
          c. the value of  (current buffer usable size*2) is larger than 16Kib
      4. the peak value is reset to the current buffer position once every **5** seconds. we maintain a new
         field in the client structure (buf_peak_last_reset_time) which is used to keep track of how long it
         passed since the last buffer peak reset.
      
      ### **Interface changes:**
      **CIENT LIST** - now contains 2 new extra fields:
      rbs= < the current size in bytes of the client reply buffer >
      rbp=< the current value in bytes of the last observed buffer peak position >
      
      **INFO STATS** - now contains 2 new statistics:
      reply_buffer_shrinks = < total number of buffer shrinks performed >
      reply_buffer_expends = < total number of buffer expends performed >
      Co-authored-by: default avatarOran Agra <oran@redislabs.com>
      Co-authored-by: default avatarYoav Steinberg <yoav@redislabs.com>
      47c51d0c
  15. 21 Feb, 2022 1 commit
    • Oran Agra's avatar
      Fix error stats and failed command stats for blocked clients (#10309) · fad0b0d2
      Oran Agra authored
      This is a followup work for #10278, and a discussion about #10279
      
      The changes:
      - fix failed_calls in command stats for blocked clients that got error.
        including CLIENT UNBLOCK, and module replying an error from a thread.
      - fix latency stats for XREADGROUP that filed with -NOGROUP
      
      Theory behind which errors should be counted:
      - error stats represents errors returned to the user, so an error handled by a
        module should not be counted.
      - total error counter should be the same.
      - command stats represents execution of commands (even with RM_Call, and if
        they fail or get rejected it counts these calls in commandstats, so it should
        also count failed_calls)
      
      Some thoughts about Scripts:
      for scripts it could be different since they're part of user code, not the infra (not an extension to redis)
      we certainly want commandstats to contain all calls and errors
      a simple script is like mult-exec transaction so an error inside it should be counted in error stats
      a script that replies with an error to the user (using redis.error_reply) should also be counted in error stats
      but then the problem is that a plain `return redis.call("SET")` should not be counted twice (once for the SET
      and once for EVAL)
      so that's something left to be resolved in #10279
      fad0b0d2
  16. 13 Feb, 2022 1 commit
    • Oran Agra's avatar
      Fix and improve module error reply statistics (#10278) · b099889a
      Oran Agra authored
      This PR handles several aspects
      1. Calls to RM_ReplyWithError from thread safe contexts don't violate thread safety.
      2. Errors returning from RM_Call to the module aren't counted in the statistics (they
        might be handled silently by the module)
      3. When a module propagates a reply it got from RM_Call to it's client, then the error
        statistics are counted.
      
      This is done by:
      1. When appending an error reply to the output buffer, we avoid updating the global
        error statistics, instead we cache that error in a deferred list in the client struct.
      2. When creating a RedisModuleCallReply object, the deferred error list is moved from
        the client into that object.
      3. when a module calls RM_ReplyWithCallReply we copy the deferred replies to the dest
        client (if that's a real client, then that's when the error statistics are updated to the server)
      
      Note about RM_ReplyWithCallReply: if the original reply had an array with errors, and the module
      replied with just a portion of the original reply, and not the entire reply, the errors are currently not
      propagated and the errors stats will not get propagated.
      
      Fix #10180
      b099889a
  17. 23 Jan, 2022 1 commit
    • Binbin's avatar
      sub-command support for ACL CAT and COMMAND LIST. redisCommand always stores fullname (#10127) · 23325c13
      Binbin authored
      
      
      Summary of changes:
      1. Rename `redisCommand->name` to `redisCommand->declared_name`, it is a
        const char * for native commands and SDS for module commands.
      2. Store the [sub]command fullname in `redisCommand->fullname` (sds).
      3. List subcommands in `ACL CAT`
      4. List subcommands in `COMMAND LIST`
      5. `moduleUnregisterCommands` now will also free the module subcommands.
      6. RM_GetCurrentCommandName returns full command name
      
      Other changes:
      1. Add `addReplyErrorArity` and `addReplyErrorExpireTime`
      2. Remove `getFullCommandName` function that now is useless.
      3. Some cleanups about `fullname` since now it is SDS.
      4. Delete `populateSingleCommand` function from server.h that is useless.
      5. Added tests to cover this change.
      6. Add some module unload tests and fix the leaks
      7. Make error messages uniform, make sure they always contain the full command
        name and that it's quoted.
      7. Fixes some typos
      
      see the history in #9504, fixes #10124
      Co-authored-by: default avatarOran Agra <oran@redislabs.com>
      Co-authored-by: default avatarguybe7 <guy.benoish@redislabs.com>
      23325c13
  18. 20 Jan, 2022 1 commit
    • perryitay's avatar
      Adding module api for processing commands during busy jobs and allow flagging... · c4b78823
      perryitay authored
      
      Adding module api for processing commands during busy jobs and allow flagging the commands that should be handled at this status (#9963)
      
      Some modules might perform a long-running logic in different stages of Redis lifetime, for example:
      * command execution
      * RDB loading
      * thread safe context
      
      During this long-running logic Redis is not responsive.
      
      This PR offers 
      1. An API to process events while a busy command is running (`RM_Yield`)
      2. A new flag (`ALLOW_BUSY`) to mark the commands that should be handled during busy
        jobs which can also be used by modules (`allow-busy`)
      3. In slow commands and thread safe contexts, this flag will start rejecting commands with -BUSY only
        after `busy-reply-threshold`
      4. During loading (`rdb_load` callback), it'll process events right away (not wait for `busy-reply-threshold`),
        but either way, the processing is throttled to the server hz rate.
      5. Allow modules to Yield to redis background tasks, but not to client commands
      
      * rename `script-time-limit` to `busy-reply-threshold` (an alias to the pre-7.0 `lua-time-limit`)
      Co-authored-by: default avatarOran Agra <oran@redislabs.com>
      c4b78823
  19. 17 Jan, 2022 1 commit
    • Oran Agra's avatar
      Set repl-diskless-sync to yes by default, add repl-diskless-sync-max-replicas (#10092) · ae899589
      Oran Agra authored
      1. enable diskless replication by default
      2. add a new config named repl-diskless-sync-max-replicas that enables
         replication to start before the full repl-diskless-sync-delay was
         reached.
      3. put replica online sooner on the master (see below)
      4. test suite uses repl-diskless-sync-delay of 0 to be faster
      5. a few tests that use multiple replica on a pre-populated master, are
         now using the new repl-diskless-sync-max-replicas
      6. fix possible timing issues in a few cluster tests (see below)
      
      put replica online sooner on the master 
      ----------------------------------------------------
      there were two tests that failed because they needed for the master to
      realize that the replica is online, but the test code was actually only
      waiting for the replica to realize it's online, and in diskless it could
      have been before the master realized it.
      
      changes include two things:
      1. the tests wait on the right thing
      2. issues in the master, putting the replica online in two steps.
      
      the master used to put the replica as online in 2 steps. the first
      step was to mark it as online, and the second step was to enable the
      write event (only after getting ACK), but in fact the first step didn't
      contains some of the tasks to put it online (like updating good slave
      count, and sending the module event). this meant that if a test was
      waiting to see that the replica is online form the point of view of the
      master, and then confirm that the module got an event, or that the
      master has enough good replicas, it could fail due to timing issues.
      
      so now the full effect of putting the replica online, happens at once,
      and only the part about enabling the writes is delayed till the ACK.
      
      fix cluster tests 
      --------------------
      I added some code to wait for the replica to sync and avoid race
      conditions.
      later realized the sentinel and cluster tests where using the original 5
      seconds delay, so changed it to 0.
      
      this means the other changes are probably not needed, but i suppose
      they're still better (avoid race conditions)
      ae899589
  20. 11 Jan, 2022 1 commit
    • Ozan Tezcan's avatar
      Reuse temporary client objects for blocked clients by module (#9940) · 6790d848
      Ozan Tezcan authored
      Added a pool for temporary client objects to reuse in module operations.
      By reusing temporary clients, we are avoiding expensive createClient()/freeClient()
      calls and improving performance of RM_BlockClient() and  RM_GetThreadSafeContext() calls. 
      
      This commit contains two optimizations: 
      
      1 - RM_BlockClient() and RM_GetThreadSafeContext() calls create temporary clients and they are freed in
      RM_UnblockClient() and RM_FreeThreadSafeContext() calls respectively. Creating/destroying client object
      takes quite time. To avoid that, added a pool of temporary clients. Pool expands when more clients are needed.
      Also, added a cron function to shrink the pool and free unused clients after some time. Pool starts with zero
      clients in it. It does not have max size and can grow unbounded as we need it. We will keep minimum of 8
      temporary clients in the pool once created. Keeping small amount of clients to avoid client allocation costs
      if temporary clients are required after some idle period.
      
      2 - After unblocking a client (RM_UnblockClient()), one byte is written to pipe to wake up Redis main thread.
      If there are many clients that will be unblocked, each operation requires one write() call which is quite expensive.
      Changed code to avoid subsequent calls if possible. 
      
      There are a few more places that need temporary client objects (e.g RM_Call()). These are now using the same
      temporary client pool to make things more centralized. 
      6790d848
  21. 10 Jan, 2022 1 commit
    • Binbin's avatar
      Make sure replicas don't write their own replies to the replication link (#10081) · a1ae260e
      Binbin authored
      The following steps will crash redis-server:
      ```
      [root]# cat crash
      PSYNC replicationid -1
      SLOWLOG GET
      GET key
      [root]# nc 127.0.0.1 6379 < crash
      ```
      
      This one following #10020 and the crash was reported in #10076.
      
      Other changes about the output info:
      1. Cmd with a full name by using `getFullCommandName`, now it will print the right
         subcommand name like `slowlog|get`.
      2. Print the full client info by using `catClientInfoString`, the info is also valuable.:
      a1ae260e
  22. 09 Jan, 2022 1 commit
    • Binbin's avatar
      Fix crash when error [sub]command name contains | (#10082) · a84c964d
      Binbin authored
      The following error commands will crash redis-server:
      ```
      > get|
      Error: Server closed the connection
      > get|set
      Error: Server closed the connection
      > get|other
      ```
      
      The reason is in #9504, we use `lookupCommandBySds` for find the
      container command. And it split the command (argv[0]) with `|`.
      If we input something like `get|other`, after the split, `get`
      will become a valid command name, pass the `ERR unknown command`
      check, and finally crash in `addReplySubcommandSyntaxError`
      
      In this case we do not need to split the command name with `|`
      and just look in the commands dict to find if `argv[0]` is a
      container command.
      
      So this commit introduce a new function call `isContainerCommandBySds`
      that it will return true if a command name is a container command.
      
      Also with the old code, there is a incorrect error message:
      ```
      > config|get set
      (error) ERR Unknown subcommand or wrong number of arguments for 'set'. Try CONFIG|GET HELP.
      ```
      
      The crash was reported in #10070.
      a84c964d
  23. 03 Jan, 2022 1 commit
  24. 02 Jan, 2022 3 commits
    • yoav-steinberg's avatar
      Make sure replicas don't write their own replies to the replication link (#10020) · 2ff3fc17
      yoav-steinberg authored
      Since #9166 we have an assertion here to make sure replica clients don't write anything to their buffer.
      But in reality a replica may attempt write data to it's buffer simply by sending a command on the replication link.
      This command in most cases will be rejected since #8868 but it'll still generate an error.
      Actually the only valid command to send on a replication link is 'REPCONF ACK` which generates no response.
      
      We want to keep the design so that replicas can send commands but we need to avoid any situation where we start
      putting data in their response buffers, especially since they aren't used anymore. This PR makes sure to disconnect
      a rogue client which generated a write on the replication link that cause something to be written to the response buffer.
      
      To recreate the bug this fixes simply connect via telnet to a redis server and write sync\r\n wait for the the payload to
      be written and then write any command (valid or invalid), such as ping\r\n on the telnet connection. It'll crash the server.
      2ff3fc17
    • Viktor Söderqvist's avatar
      Wait for replicas when shutting down (#9872) · 45a155bd
      Viktor Söderqvist authored
      
      
      To avoid data loss, this commit adds a grace period for lagging replicas to
      catch up the replication offset.
      
      Done:
      
      * Wait for replicas when shutdown is triggered by SIGTERM and SIGINT.
      
      * Wait for replicas when shutdown is triggered by the SHUTDOWN command. A new
        blocked client type BLOCKED_SHUTDOWN is introduced, allowing multiple clients
        to call SHUTDOWN in parallel.
        Note that they don't expect a response unless an error happens and shutdown is aborted.
      
      * Log warning for each replica lagging behind when finishing shutdown.
      
      * CLIENT_PAUSE_WRITE while waiting for replicas.
      
      * Configurable grace period 'shutdown-timeout' in seconds (default 10).
      
      * New flags for the SHUTDOWN command:
      
          - NOW disables the grace period for lagging replicas.
      
          - FORCE ignores errors writing the RDB or AOF files which would normally
            prevent a shutdown.
      
          - ABORT cancels ongoing shutdown. Can't be combined with other flags.
      
      * New field in the output of the INFO command: 'shutdown_in_milliseconds'. The
        value is the remaining maximum time to wait for lagging replicas before
        finishing the shutdown. This field is present in the Server section **only**
        during shutdown.
      
      Not directly related:
      
      * When shutting down, if there is an AOF saving child, it is killed **even** if AOF
        is disabled. This can happen if BGREWRITEAOF is used when AOF is off.
      
      * Client pause now has end time and type (WRITE or ALL) per purpose. The
        different pause purposes are *CLIENT PAUSE command*, *failover* and
        *shutdown*. If clients are unpaused for one purpose, it doesn't affect client
        pause for other purposes. For example, the CLIENT UNPAUSE command doesn't
        affect client pause initiated by the failover or shutdown procedures. A completed
        failover or a failed shutdown doesn't unpause clients paused by the CLIENT
        PAUSE command.
      
      Notes:
      
      * DEBUG RESTART doesn't wait for replicas.
      
      * We already have a warning logged when a replica disconnects. This means that
        if any replica connection is lost during the shutdown, it is either logged as
        disconnected or as lagging at the time of exit.
      Co-authored-by: default avatarOran Agra <oran@redislabs.com>
      45a155bd
    • yoav-steinberg's avatar
      Generate RDB with Functions only via redis-cli --functions-rdb (#9968) · 1bf6d6f1
      yoav-steinberg authored
      
      
      This is needed in order to ease the deployment of functions for ephemeral cases, where user
      needs to spin up a server with functions pre-loaded.
      
      #### Details:
      
      * Added `--functions-rdb` option to _redis-cli_.
      * Functions only rdb via `REPLCONF rdb-filter-only functions`. This is a placeholder for a space
        separated inclusion filter for the RDB. In the future can be `REPLCONF rdb-filter-only
        "functions db:3 key-patten:user*"` and a complementing `rdb-filter-exclude` `REPLCONF`
        can also be added.
      * Handle "slave requirements" specification to RDB saving code so we can use the same RDB
        when different slaves express the same requirements (like functions-only) and not share the
        RDB when their requirements differ. This is currently just a flags `int`, but can be extended to
        a more complex structure with various filter fields.
      * make sure to support filters only in diskless replication mode (not to override the persistence file),
        we do that by forcing diskless (even if disabled by config)
      
      other changes:
      * some refactoring in rdb.c (extract portion of a big function to a sub-function)
      * rdb_key_save_delay used in AOFRW too
      * sendChildInfo takes the number of updated keys (incremental, rather than absolute)
      Co-authored-by: default avatarOran Agra <oran@redislabs.com>
      1bf6d6f1
  25. 22 Dec, 2021 2 commits
    • guybe7's avatar
      Sort out mess around propagation and MULTI/EXEC (#9890) · 7ac21307
      guybe7 authored
      The mess:
      Some parts use alsoPropagate for late propagation, others using an immediate one (propagate()),
      causing edge cases, ugly/hacky code, and the tendency for bugs
      
      The basic idea is that all commands are propagated via alsoPropagate (i.e. added to a list) and the
      top-most call() is responsible for going over that list and actually propagating them (and wrapping
      them in MULTI/EXEC if there's more than one command). This is done in the new function,
      propagatePendingCommands.
      
      Callers to propagatePendingCommands:
      1. top-most call() (we want all nested call()s to add to the also_propagate array and just the top-most
         one to propagate them) - via `afterCommand`
      2. handleClientsBlockedOnKeys: it is out of call() context and it may propagate stuff - via `afterCommand`. 
      3. handleClientsBlockedOnKeys edge case: if the looked-up key is already expired, we will propagate the
         expire but will not unblock any client so `afterCommand` isn't called. in that case, we have to propagate
         the deletion explicitly.
      4. cron stuff: active-expire and eviction may also propagate stuff
      5. modules: the module API allows to propagate stuff from just about anywhere (timers, keyspace notifications,
         threads). I could have tried to catch all the out-of-call-context places but it seemed easier to handle it in one
         place: when we free the context. in the spirit of what was done in call(), only the top-most freeing of a module
         context may cause propagation.
      6. modules: when using a thread-safe ctx it's not clear when/if the ctx will be freed. we do know that the module
         must lock the GIL before calling RM_Replicate/RM_Call so we propagate the pending commands when
         releasing the GIL.
      
      A "known limitation", which were actually a bug, was fixed because of this commit (see propagate.tcl):
         When using a mix of RM_Call with `!` and RM_Replicate, the command would propagate out-of-order:
         first all the commands from RM_Call, and then the ones from RM_Replicate
      
      Another thing worth mentioning is that if, in the past, a client would issue a MULTI/EXEC with just one
      write command the server would blindly propagate the MULTI/EXEC too, even though it's redundant.
      not anymore.
      
      This commit renames propagate() to propagateNow() in order to cause conflicts in pending PRs.
      propagatePendingCommands is the only caller of propagateNow, which is now a static, internal helper function.
      
      Optimizations:
      1. alsoPropagate will not add stuff to also_propagate if there's no AOF and replicas
      2. alsoPropagate reallocs also_propagagte exponentially, to save calls to memmove
      
      Bugfixes:
      1. CONFIG SET can create evictions, sending notifications which can cause to dirty++ with modules.
         we need to prevent it from propagating to AOF/replicas
      2. We need to set current_client in RM_Call. buggy scenario:
         - CONFIG SET maxmemory, eviction notifications, module hook calls RM_Call
         - assertion in lookupKey crashes, because current_client has CONFIG SET, which isn't CMD_WRITE
      3. minor: in eviction, call propagateDeletion after notification, like active-expire and all commands
         (we always send a notification before propagating the command)
      7ac21307
    • Oran Agra's avatar
      Allow most CONFIG SET during loading, block some commands in async-loading (#9878) · 41e6e05d
      Oran Agra authored
      ## background
      Till now CONFIG SET was blocked during loading.
      (In the not so distant past, GET was disallowed too)
      
      We recently (not released yet) added an async-loading mode, see #9323,
      and during that time it'll serve CONFIG SET and any other command.
      And now we realized (#9770) that some configs, and commands are dangerous
      during async-loading.
      
      ## changes
      * Allow most CONFIG SET during loading (both on async-loading and normal loading)
      * Allow CONFIG REWRITE and CONFIG RESETSTAT during loading
      * Block a few config during loading (`appendonly`, `repl-diskless-load`, and `dir`)
      * Block a few commands during loading (list below)
      
      ## the blocked commands:
      * SAVE - obviously we don't wanna start a foregreound save during loading 8-)
      * BGSAVE - we don't mind to schedule one, but we don't wanna fork now
      * BGREWRITEAOF - we don't mind to schedule one, but we don't wanna fork now
      * MODULE - we obviously don't wanna unload a module during replication / rdb loading
        (MODULE HELP and MODULE LIST are not blocked)
      * SYNC / PSYNC - we're in the middle of RDB loading from master, must not allow sync
        requests now.
      * REPLICAOF / SLAVEOF - we're in the middle of replicating, maybe it makes sense to let
        the user abort it, but he couldn't do that so far, i don't wanna take any risk of bugs due to odd state.
      * CLUSTER - only allow [HELP, SLOTS, NODES, INFO, MYID, LINKS, KEYSLOT, COUNTKEYSINSLOT,
        GETKEYSINSLOT, RESET, REPLICAS, COUNT_FAILURE_REPORTS], for others, preserve the status quo
      
      ## other fixes
      * processEventsWhileBlocked had an issue when being nested, this could happen with a busy script
        during async loading (new), but also in a busy script during AOF loading (old). this lead to a crash in
        the scenario described in #6988
      41e6e05d
  26. 19 Dec, 2021 1 commit
    • YaacovHazan's avatar
      Protected configs and sensitive commands (#9920) · ae2f5b7b
      YaacovHazan authored
      Block sensitive configs and commands by default.
      
      * `enable-protected-configs` - block modification of configs with the new `PROTECTED_CONFIG` flag.
         Currently we add this flag to `dbfilename`, and `dir` configs,
         all of which are non-mutable configs that can set a file redis will write to.
      * `enable-debug-command` - block the `DEBUG` command
      * `enable-module-command` - block the `MODULE` command
      
      These have a default value set to `no`, so that these features are not
      exposed by default to client connections, and can only be set by modifying the config file.
      
      Users can change each of these to either `yes` (allow all access), or `local` (allow access from
      local TCP connections and unix domain connections)
      
      Note that this is a **breaking change** (specifically the part about MODULE command being disabled by default).
      I.e. we don't consider DEBUG command being blocked as an issue (people shouldn't have been using it),
      and the few configs we protected are unlikely to have been set at runtime anyway.
      On the other hand, it's likely to assume some users who use modules, load them from the config file anyway.
      Note that's the whole point of this PR, for redis to be more secure by default and reduce the attack surface on
      innocent users, so secure defaults will necessarily mean a breaking change.
      ae2f5b7b
  27. 15 Dec, 2021 1 commit
    • guybe7's avatar
      Auto-generate the command table from JSON files (#9656) · 86781600
      guybe7 authored
      Delete the hardcoded command table and replace it with an auto-generated table, based
      on a JSON file that describes the commands (each command must have a JSON file).
      
      These JSON files are the SSOT of everything there is to know about Redis commands,
      and it is reflected fully in COMMAND INFO.
      
      These JSON files are used to generate commands.c (using a python script), which is then
      committed to the repo and compiled.
      
      The purpose is:
      * Clients and proxies will be able to get much more info from redis, instead of relying on hard coded logic.
      * drop the dependency between Redis-user and the commands.json in redis-doc.
      * delete help.h and have redis-cli learn everything it needs to know just by issuing COMMAND (will be
        done in a separate PR)
      * redis.io should stop using commands.json and learn everything from Redis (ultimately one of the release
        artifacts should be a large JSON, containing all the information about all of the commands, which will be
        generated from COMMAND's reply)
      * the byproduct of this is:
        * module commands will be able to provide that info and possibly be more of a first-class citizens
        * in theory, one may be able to generate a redis client library for a strictly typed language, by using this info.
      
      ### Interface changes
      
      #### COMMAND INFO's reply change (and arg-less COMMAND)
      
      Before this commit the reply at index 7 contained the key-specs list
      and reply at index 8 contained the sub-commands list (Both unreleased).
      Now, reply at index 7 is a map of:
      - summary - short command description
      - since - debut version
      - group - command group
      - complexity - complexity string
      - doc-flags - flags used for documentation (e.g. "deprecated")
      - deprecated-since - if deprecated, from which version?
      - replaced-by - if deprecated, which command replaced it?
      - history - a list of (version, what-changed) tuples
      - hints - a list of strings, meant to provide hints for clients/proxies. see https://github.com/redis/redis/issues/9876
      - arguments - an array of arguments. each element is a map, with the possibility of nesting (sub-arguments)
      - key-specs - an array of keys specs (already in unstable, just changed location)
      - subcommands - a list of sub-commands (already in unstable, just changed location)
      - reply-schema - will be added in the future (see https://github.com/redis/redis/issues/9845)
      
      more details on these can be found in https://github.com/redis/redis-doc/pull/1697
      
      only the first three fields are mandatory 
      
      #### API changes (unreleased API obviously)
      
      now they take RedisModuleCommand opaque pointer instead of looking up the command by name
      
      - RM_CreateSubcommand
      - RM_AddCommandKeySpec
      - RM_SetCommandKeySpecBeginSearchIndex
      - RM_SetCommandKeySpecBeginSearchKeyword
      - RM_SetCommandKeySpecFindKeysRange
      - RM_SetCommandKeySpecFindKeysKeynum
      
      Currently, we did not add module API to provide additional information about their commands because
      we couldn't agree on how the API should look like, see https://github.com/redis/redis/issues/9944
      
      .
      
      ### Somehow related changes
      1. Literals should be in uppercase while placeholder in lowercase. Now all the GEO* command
         will be documented with M|KM|FT|MI and can take both lowercase and uppercase
      
      ### Unrelated changes
      1. Bugfix: no_madaory_keys was absent in COMMAND's reply
      2. expose CMD_MODULE as "module" via COMMAND
      3. have a dedicated uint64 for ACL categories (instead of having them in the same uint64 as command flags)
      Co-authored-by: default avatarItamar Haber <itamar@garantiadata.com>
      86781600
  28. 01 Dec, 2021 2 commits
    • meir@redislabs.com's avatar
      Redis Functions - Introduce script unit. · fc731bc6
      meir@redislabs.com authored
      Script unit is a new unit located on script.c.
      Its purpose is to provides an API for functions (and eval)
      to interact with Redis. Interaction includes mostly
      executing commands, but also functionalities like calling
      Redis back on long scripts or check if the script was killed.
      
      The interaction is done using a scriptRunCtx object that
      need to be created by the user and initialized using scriptPrepareForRun.
      
      Detailed list of functionalities expose by the unit:
      1. Calling commands (including all the validation checks such as
         acl, cluster, read only run, ...)
      2. Set Resp
      3. Set Replication method (AOF/REPLICATION/NONE)
      4. Call Redis back to on long running scripts to allow Redis reply
         to clients and perform script kill
      
      The commit introduce the new unit and uses it on eval commands to
      interact with Redis.
      fc731bc6
    • meir@redislabs.com's avatar
      Redis Functions - Move Lua related variable into luaCtx struct · e0cd580a
      meir@redislabs.com authored
      The following variable was renamed:
      1. lua_caller 			-> script_caller
      2. lua_time_limit 		-> script_time_limit
      3. lua_timedout 		-> script_timedout
      4. lua_oom 			-> script_oom
      5. lua_disable_deny_script 	-> script_disable_deny_script
      6. in_eval			-> in_script
      
      The following variables was moved to lctx under eval.c
      1.  lua
      2.  lua_client
      3.  lua_cur_script
      4.  lua_scripts
      5.  lua_scripts_mem
      6.  lua_replicate_commands
      7.  lua_write_dirty
      8.  lua_random_dirty
      9.  lua_multi_emitted
      10. lua_repl
      11. lua_kill
      12. lua_time_start
      13. lua_time_snapshot
      
      This commit is in a low risk of introducing any issues and it
      is just moving varibales around and not changing any logic.
      e0cd580a
  29. 29 Nov, 2021 1 commit
  30. 23 Nov, 2021 1 commit
    • guybe7's avatar
      QUIT is a command, HOST: and POST are not (#9798) · b161cff5
      guybe7 authored
      Some people complain that QUIT is missing from help/command table.
      Not appearing in COMMAND command, command stats, ACL, etc.
      and instead, there's a hack in processCommand with a comment that looks outdated.
      Note that it is [documented](https://redis.io/commands/quit)
      
      At the same time, HOST: and POST are there in the command table although these are not real commands.
      They would appear in the COMMAND command, and even in commandstats.
      
      Other changes:
      1. Initialize the static logged_time static var in securityWarningCommand
      2. add `no-auth` flag to RESET so it can always be executed.
      b161cff5
  31. 21 Nov, 2021 1 commit
    • Yossi Gottlieb's avatar
      Fix occasional RM_Call() crashes. (#9805) · fd0ca747
      Yossi Gottlieb authored
      With dynamically growing argc (#9528), it is necessary to initialize
      argv_len. Normally createClient() handles that, but in the case of a
      module shared_client, this needs to be done explicitly.
      
      This also addresses an issue with rewriteClientCommandArgument() which
      doesn't properly handle the case where the new element extends beyond
      argc but not beyond argv_len.
      fd0ca747
  32. 11 Nov, 2021 1 commit
    • Ozan Tezcan's avatar
      Add sanitizer support and clean up sanitizer findings (#9601) · b91d8b28
      Ozan Tezcan authored
      - Added sanitizer support. `address`, `undefined` and `thread` sanitizers are available.  
      - To build Redis with desired sanitizer : `make SANITIZER=undefined`
      - There were some sanitizer findings, cleaned up codebase
      - Added tests with address and undefined behavior sanitizers to daily CI.
      - Added tests with address sanitizer to the per-PR CI (smoke out mem leaks sooner).
      
      Basically, there are three types of issues : 
      
      **1- Unaligned load/store** : Most probably, this issue may cause a crash on a platform that
      does not support unaligned access. Redis does unaligned access only on supported platforms.
      
      **2- Signed integer overflow.** Although, signed overflow issue can be problematic time to time
      and change how compiler generates code, current findings mostly about signed shift or simple
      addition overflow. For most platforms Redis can be compiled for, this wouldn't cause any issue
      as far as I can tell (checked generated code on godbolt.org).
      
       **3 -Minor leak** (redis-cli), **use-after-free**(just before calling exit());
      
      UB means nothing guaranteed and risky to reason about program behavior but I don't think any
      of the fixes here worth backporting. As sanitizers are now part of the CI, preventing new issues
      will be the real benefit. 
      b91d8b28
  33. 25 Oct, 2021 1 commit
    • Wang Yuan's avatar
      Replication backlog and replicas use one global shared replication buffer (#9166) · c1718f9d
      Wang Yuan authored
      ## Background
      For redis master, one replica uses one copy of replication buffer, that is a big waste of memory,
      more replicas more waste, and allocate/free memory for every reply list also cost much.
      If we set client-output-buffer-limit small and write traffic is heavy, master may disconnect with
      replicas and can't finish synchronization with replica. If we set  client-output-buffer-limit big,
      master may be OOM when there are many replicas that separately keep much memory.
      Because replication buffers of different replica client are the same, one simple idea is that
      all replicas only use one replication buffer, that will effectively save memory.
      
      Since replication backlog content is the same as replicas' output buffer, now we
      can discard replication backlog memory and use global shared replication buffer
      to implement replication backlog mechanism.
      
      ## Implementation
      I create one global "replication buffer" which contains content of replication stream.
      The structure of "replication buffer" is similar to the reply list that exists in every client.
      But the node of list is `replBufBlock`, which has `id, repl_offset, refcount` fields.
      ```c
      /* Replication buffer blocks is the list of replBufBlock.
       *
       * +--------------+       +--------------+       +--------------+
       * | refcount = 1 |  ...  | refcount = 0 |  ...  | refcount = 2 |
       * +--------------+       +--------------+       +--------------+
       *      |                                            /       \
       *      |                                           /         \
       *      |                                          /           \
       *  Repl Backlog                               Replia_A      Replia_B
       * 
       * Each replica or replication backlog increments only the refcount of the
       * 'ref_repl_buf_node' which it points to. So when replica walks to the next
       * node, it should first increase the next node's refcount, and when we trim
       * the replication buffer nodes, we remove node always from the head node which
       * refcount is 0. If the refcount of the head node is not 0, we must stop
       * trimming and never iterate the next node. */
      
      /* Similar with 'clientReplyBlock', it is used for shared buffers between
       * all replica clients and replication backlog. */
      typedef struct replBufBlock {
          int refcount;           /* Number of replicas or repl backlog using. */
          long long id;           /* The unique incremental number. */
          long long repl_offset;  /* Start replication offset of the block. */
          size_t size, used;
          char buf[];
      } replBufBlock;
      ```
      So now when we feed replication stream into replication backlog and all replicas, we only need
      to feed stream into replication buffer `feedReplicationBuffer`. In this function, we set some fields of
      replication backlog and replicas to references of the global replication buffer blocks. And we also
      need to check replicas' output buffer limit to free if exceeding `client-output-buffer-limit`, and trim
      replication backlog if exceeding `repl-backlog-size`.
      
      When sending reply to replicas, we also need to iterate replication buffer blocks and send its
      content, when totally sending one block for replica, we decrease current node count and
      increase the next current node count, and then free the block which reference is 0 from the
      head of replication buffer blocks.
      
      Since now we use linked list to manage replication backlog, it may cost much time for iterating
      all linked list nodes to find corresponding replication buffer node. So we create a rax tree to
      store some nodes  for index, but to avoid rax tree occupying too much memory, i record
      one per 64 nodes for index.
      
      Currently, to make partial resynchronization as possible as much, we always let replication
      backlog as the last reference of replication buffer blocks, backlog size may exceeds our setting
      if slow replicas that reference vast replication buffer blocks, and this method doesn't increase
      memory usage since they share replication buffer. To avoid freezing server for freeing unreferenced
      replication buffer blocks when we need to trim backlog for exceeding backlog size setting,
      we trim backlog incrementally (free 64 blocks per call now), and make it faster in
      `beforeSleep` (free 640 blocks).
      
      ### Other changes
      - `mem_total_replication_buffers`: we add this field in INFO command, it means the total
        memory of replication buffers used.
      - `mem_clients_slaves`:  now even replica is slow to replicate, and its output buffer memory
        is not 0, but it still may be 0, since replication backlog and replicas share one global replication
        buffer, only if replication buffer memory is more than the repl backlog setting size, we consider
        the excess as replicas' memory. Otherwise, we think replication buffer memory is the consumption
        of repl backlog.
      - Key eviction
        Since all replicas and replication backlog share global replication buffer, we think only the
        part of exceeding backlog size the extra separate consumption of replicas.
        Because we trim backlog incrementally in the background, backlog size may exceeds our
        setting if slow replicas that reference vast replication buffer blocks disconnect.
        To avoid massive eviction loop, we don't count the delayed freed replication backlog into
        used memory even if there are no replicas, i.e. we also regard this memory as replicas's memory.
      - `client-output-buffer-limit` check for replica clients
        It doesn't make sense to set the replica clients output buffer limit lower than the repl-backlog-size
        config (partial sync will succeed and then replica will get disconnected). Such a configuration is
        ignored (the size of repl-backlog-size will be used). This doesn't have memory consumption
        implications since the replica client will share the backlog buffers memory.
      - Drop replication backlog after loading data if needed
        We always create replication backlog if server is a master, we need it because we put DELs in
        it when loading expired keys in RDB, but if RDB doesn't have replication info or there is no rdb,
        it is not possible to support partial resynchronization, to avoid extra memory of replication backlog,
        we drop it.
      - Multi IO threads
       Since all replicas and replication backlog use global replication buffer,  if I/O threads are enabled,
        to guarantee data accessing thread safe, we must let main thread handle sending the output buffer
        to all replicas. But before, other IO threads could handle sending output buffer of all replicas.
      
      ## Other optimizations
      This solution resolve some other problem:
      - When replicas disconnect with master since of out of output buffer limit, releasing the output
        buffer of replicas may freeze server if we set big `client-output-buffer-limit` for replicas, but now,
        it doesn't cause freezing.
      - This implementation may mitigate reply list copy cost time(also freezes server) when one replication
        has huge reply buffer and another replica can copy buffer for full synchronization. now, we just copy
        reference info, it is very light.
      - If we set replication backlog size big, it also may cost much time to copy replication backlog into
        replica's output buffer. But this commit eliminates this problem.
      - Resizing replication backlog size doesn't empty current replication backlog content.
      c1718f9d